Sanjog S. Nagarkar

Highly Selective Detection of Nitro Explosives by a Luminescent Metal–Organic Framework†

Fluorescence-baseddetection is gaining increasing attention owing to its highsensitivity, simplicity, short response time, and its ability to beemployed both in solution and solid phase. Numerousp-electron-rich fluorescent conjugated polymers have beensynthesized, and are used in the detection of trace amounts ofnitro aromatics.

Two‐in‐One: Inherent Anhydrous and Water‐Assisted High Proton Conduction in a 3D Metal–Organic Framework

The development of solid-state proton-conducting materials with high conductivity that operate under both anhydrous and humidified conditions is currently of great interest in fuel-cell technology. A 3D metal-organic framework (MOF) with acid-base pairs in its coordination space that efficiently conducts protons under both anhydrous and humid conditions has now been developed. The anhydrous proton conductivity for this MOF is among the highest values that have been reported for MOF materials, whereas its water-assisted proton conductivity is comparable to that of the organic polymer Nafion, which is currently used for practical applications. Unlike other MOFs, which conduct protons either under anhydrous or humid conditions, this compound should represent a considerable advance in the development of efficient solid-state proton-conducting materials that work under both anhydrous and humid conditions.

Selective CO2 Adsorption in a Robust and Water-Stable Porous Coordination Polymer with New Network Topology

A robust and water-stable porous coordination polymer [Cd(NDC)(0.5)(PCA)]·G(x) (1) (H(2)NDC = 2,6-napthalenedicarboxylic acid, HPCA = 4-pyridinecarboxylic acid, G = guest molecules) with new network topology has been synthesized solvothermally. The framework is 3D porous material and forms a 1D channel along the c-axis, with the channel dimensions ~9.48 × 7.83 Å(2). The compound has high selectivity in uptake of CO(2) over other gases (H(2), O(2), Ar, N(2), and CH(4)). The framework is highly stable in presence of water vapor even at 60 °C. The high CO(2) selectivity over other gases and water stability makes the compound promising candidate for industrial postcombustion gas separation application.

Engineering metal–organic frameworks for aqueous phase 2,4,6-trinitrophenol (TNP) sensing

2,4,6-Trinitrophenol (TNP) is a highly explosive molecule that is also widely used in industrial processing on a large scale. During synthesis, processing and disposal, TNP is released to the environment especially to water streams, contaminating ground and surface water. TNP and its biologically transformed products like picramic acids have been identified as highly toxic species to biota and may lead to chronic diseases such as sycosis and cancer. Thus, aqueous phase detection of TNP becomes an imperative aspect for the design of any potential sensor. Metal–organic frameworks (MOFs) have emerged as an important class of sensors owing to their permanent porosity, designability and variety of signal transduction pathways. Luminescent MOFs (LMOFs) have shown great potential as sensors for various nitro explosives by modulation of their luminescence behaviour in the presence of nitro explosives. Most of the LMOFs detect nitro explosives in the vapour phase and/or in organic solvents while aqueous phase detection is rarely investigated. Herein we present recent developments in the area of LMOFs for aqueous phase TNP sensing and discuss strategies used to improve the sensing performance. Finally, based on our perspective, important aspects of LMOF performance needing immediate attention for future developments are provided.

Metal-organic framework based highly selective fluorescence turn-on probe for hydrogen sulphide

Hydrogen sulphide (H2S) is known to play a vital role in human physiology and pathology which stimulated interest in understanding complex behaviour of H2S. Discerning the pathways of H2S production and its mode of action is still a challenge owing to its volatile and reactive nature. Herein we report azide functionalized metal-organic framework (MOF) as a selective turn-on fluorescent probe for H2S detection. The MOF shows highly selective and fast response towards H2S even in presence of other relevant biomolecules. Low cytotoxicity and H2S detection in live cells, demonstrate the potential of MOF towards monitoring H2S chemistry in biological system. To the best of our knowledge this is the first example of MOF that exhibit fast and highly selective fluorescence turn-on response towards H2S under physiological conditions.

A Nitro-Functionalized Metal–Organic Framework as a Reaction-Based Fluorescence Turn-On Probe for Rapid and Selective H2S Detection

The toxic gas H2 S has recently emerged as one of the important signaling molecules in biological systems. Thus understanding the production, distribution, and mode of action of H2 S in biological system is important, but the fleeting and reactive nature of H2 S makes it a daunting task. Herein we report a biocompatible, nitro-functionalized metal-organic framework as reaction-based fluorescence turn-on probe for fast and selective H2 S detection. The selective turn-on performance of MOF remains unaffected even in presence of competing biomolecules.

Bi-porous metal–organic framework with hydrophilic and hydrophobic channels: selective gas sorption and reversible iodine uptake studies

A new three-dimensional (3D) bi-porous metal–organic framework (MOF), {[(Me2NH2)2]·[Cd3(5-tbip)4]·2DMF}n (1) (5-tbipH2: 5-tert-butylisophthalic acid) has been synthesized. The 5-tbip ligand containing a hydrophobic t-butyl group and hydrophilic carboxylate groups is used to synthesize the bi-porous framework. This 3D MOF contains two types of channels, a wide mouth hydrophilic channel of dimension 7.448 × 7.676 A2 and a narrow mouth hydrophobic channel of dimension 2.33 × 1.926 A2. Hydrophilic channels are lined with the orderly arranged dimethyl ammonium (DMA) cations which neutralize the anionic 3D framework. The guest-free form of the MOF (1′) showed interesting CO2 selectivity over other gases such as N2, CH4, and H2. Since the effective pore size of the desolvated compound 1′ (∼0.6 nm: from the pore size distribution curve of CO2 adsorption measurement) is much more than the kinetic diameter of all measured gases (CO2 = 3.3 A, CH4 = 3.76 A, N2 = 3.64 A and H2 = 2.8 A), selective capture of CO2 by 1′ could be ascribed to the strong electrostatic interaction of CO2 with the framework. Compound 1′ also shows reversible iodine uptake (1′ ⊂ 4I2: based on the sample weight measurements and TGA data) with visible color change of the compound. Interestingly, the iodine-loaded MOF showed ∼76 times increase in electrical conductivity compared to 1′.

Amino Acid Based Dynamic Metal–Biomolecule Frameworks

On the move: Two isostructural, homochiral Cu(II) coordination frameworks based on amino acids (D- and L-PGA) were synthesized. Dynamic behavior by solid-state structural transformation in single-crystal-to-single-crystal fashion was demonstrated. The extent of structural dynamism was shown by guest inclusion studies. Reversible sol-gel formation and anion-tuning morphology of the compounds is also discussed.

Increase in Electrical Conductivity of MOF to Billion-Fold upon Filling the Nanochannels with Conducting Polymer

Redox-active pyrrole (Py) monomers were intercalated into 1D nanochannels of [Cd(NDC)0.5(PCA)]·Gx (H2NDC = 2,6-napthalenedicarboxylic acid, HPCA = 4-pyridinecarboxylic acid, G = guest molecules) (1) - a fluorescent 3D MOF (λem = 385 nm). Subsequent activation of 1⊃Py upon immersing into iodine (I2) solution resulted in an increment of the bulk electrical conductivity by ∼9 orders of magnitude. The unusual increase in conductivity was attributed to the formation of highly oriented and conducting polypyrrole (PPy) chains inside 1D nanochannels and specific host-guest interaction in 1⊃PPy thereof. The Hall-effect measurements suggested 1⊃PPy to be an n-type semiconductor material with remarkably high-carrier density (η) of ∼1.5 × 10(17) cm(-3) and mobility (μ) of ∼8.15 cm(2) V(-1) s(-1). The fluorescence property of 1 was almost retained in 1⊃PPy with concomitant exciplex-type emission at higher wavelength (λem = 520 nm). The here-presented results on [MOF⊃Conducting Polymer] systems in general will serve as a prototype experiment toward rational design for the development of highly conductive yet fluorescent MOF-based materials for various optoelectronic applications.

Bistable dynamic coordination polymer showing reversible structural and functional transformations.

A bistable dynamic coordination polymer [Ni(pca)(bdc)(0.5)(H(2)O)(2)] having a two-dimensional (2D) zigzag sheet structure is synthesized solvothermally. Topological analysis revealed that the frameworks have an hcb type of uninodal net. The compound exhibits guest specific reversible structural transformations accompanying reversible changes in physical properties driven by inherent flexibility and transformability.